This invention relates to an extrusion-forming jig for use in extruding a ceramic material to form ceramic honeycomb structures.
Extrusion-forming jigs such as masks, rings and the like have been used, at a location downstream of dies for extruding ceramic materials to form honeycomb structures. As disclosed in, for example, Japanese Utility Model Application Laid-open No. 49-8,559, such jigs are used to form outer walls of honeycomb structures made of ceramic batches, or the like, passing through dies, or to regulate sectional shapes and external dimensions of honeycomb structures.
The surfaces of such extrusion-forming jigs contact ceramic batches and are likely to be abraded. However, honeycomb structures are required to be formed within extreme dimensional tolerances. Therefore it has been necessary to treat at least the surfaces of the jigs which contact ceramic batches by surface treatments such as plating, to obtain wear-resistant surfaces.
However, even if the surfaces of the jigs contacting ceramic batches are treated by surface treatments such as plating for the purpose of improving the wear-resistance of the jigs, the improved wear-resistance is not always sufficient. Therefore, extrusion-forming jigs having much higher wear-resistance have been desired for many years.
In the case of applying a surface treatment to jigs in the conventional manner, however, the jigs are generally treated at high temperatures. Therefore, strains were produced in the surfaces of jigs which were subjected to such a surface treatment thus detrimentally affecting their dimensions and accuracy. As a result, it is disadvantageously required to correct the altered dimensions and accuracy of the jigs. Moreover surface treatments such as plating increase the man-hours necessary for producing the jigs.